Switching regulator control circuit, switching regulator using the circuit, and switching signal generating apparatus

ABSTRACT

A switching regulator includes a first switching regulator corresponding to a master channel, and a second switching regulator corresponding to a slave channel. The first switching regulator generates first output voltage Vout 1  by a constant on-time system in which on-time is constant. On the other hand, the second switching regulator monitors a first switching signal and a second on-time control circuit determines on-time of a second switching signal in accordance with lapse time from the rising time of the first switching signal to the rising time of a second switching signal.

CROSS REFERENCE TO RELATED APPLICATIONS

This is a U.S. national stage of application No. PCT/JP2005/017350,filed on 21 Sep. 2005. Priority under 35 U.S.C. §119(a) and U.S.C.§365(b) is claimed from Japanese Application No. 2004-316606, filed 29Oct. 2004, the disclosure of which is also incorporated herein byreference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a power supply apparatus and, moreparticularly, to a switching regulator.

2. Description of the Related Art

In various electronic devices, in order to supply a proper voltage to anelectronic circuit internally used, a step-up-type or step-down-typeDC/DC converter such as a switching regulator is widely used. Such aswitching regulator has a switching regulator control circuit forgenerating a switching signal for controlling on/off of a switchingelement.

As a switching signal, a PWM (Pulse Width Modulation) signal having aconstant frequency for turning on/off the switching element inaccordance with a pulse width is widely used (refer to Patent Documents1 and 2). In a constant frequency system using such a PWM signal, aperiod since a switching element is turned on until it is turned on nextis made constant to a cycle time given by the inverse number of aswitching frequency. Consequently, there is a problem that the systemcannot follow a load fluctuation and a fluctuation in the input voltagehigher than the switching frequency, and an output is accordinglyunstable.

To address an application requesting high-speed load response, a systemin which the pulse width of a switching signal, that is, on-time Ton isconstant and a timing at which the switching signal becomes the highlevel or the frequency is changed (hereinafter, referred to as constanton-time system) is considered. The constant on-time system can respondto the load fluctuation and input voltage fluctuation at higher speed ascompared with the constant frequency system.

[Patent Document 1] Japanese Patent Application Laid-open No.2003-219638

[Patent Document 2] Japanese Patent Application Laid-open No.2003-319643

There is a case that an electronic device on which such a switchingregulator is mounted needs a plurality of different voltages, and astep-down switching regulator is provided with a plurality of channels,drops the same input voltage at different dropping ratios, and outputsthe dropped voltages. In this case, switching signals in a plurality ofchannels are turned on simultaneously. When switching elements of thechannels are turned on simultaneously, an instantaneous value of inputcurrent supplied from an input power source for supplying input voltagesuddenly increases. When fluctuations of the input current of thestep-down switching regulator increase, the current capacitance of theinput power source has to be increased or the capacitance of an inputcapacitor for smoothing has to be increased. Further, when the inputcurrent increases instantaneously, switching noise increases. It causesproblems of erroneous operation of peripheral circuits and increase inEMI (Electro Magnetic Interference).

The problems will be considered with respect to switching regulators oftwo systems. The duty ratio “Duty” of the step-down switching regulatoris given by the relation Vout/Vin(Duty=Vout/Vin) in a steady state. Inthe constant frequency system using the PWM signal, switching signals ofa plurality of channels can be generated from a single oscillator, andthe frequency of the plurality of switching signals can be the sameirrespective of the duty ratio. Consequently, synchronization among theplurality of channels can be easily obtained, and the timing at whichthe switching signal is turned on can be easily shifted. On the otherhand, in the case of a switching regulator of the constant on-timesystem, when the on-times Ton of switching signals in channels are setto be equal, the frequencies of the switching signals change as the dutyratio changes. It becomes difficult to obtain synchronization of thechannels, and there is the possibility that a plurality of switchingsignals are turned on simultaneously. Therefore, in the case of usingswitching regulator of the constant on-time system in a plurality ofchannels, a problem of increase in the input current or EMI increasesoccurs.

SUMMARY OF THE INVENTION

The present invention has been achieved in view of the problems and ageneral purpose of the invention is to provide a switching regulator ofconstant on-time system in which synchronous control can be performedamong a plurality of channels.

An embodiment of the present invention relates to a switching regulatorcontrol circuit. The switching regulator control circuit includes: afirst switching signal generating circuit which generates a firstswitching signal for driving a first switching element connected to afirst output circuit; and a second switching signal generating circuitwhich generates a second switching signal for driving a second switchingelement connected to a second output circuit. The first switching signalgenerating circuit changes a timing at which the first switching signalis turned on so that first output voltage output from the first outputcircuit becomes close to predetermined first reference voltage whilemaking on-time of the first switching signal predetermined constantfirst on-time. On the other hand, the second switching signal generatingcircuit changes on-time of the second switching signal so that frequencyof the second switching signal becomes close to frequency of the firstswitching signal, and changes a timing at which the second switchingsignal is turned on so that second output voltage output from the secondoutput circuit becomes close to predetermined second reference voltage.

According to the embodiment, by adjusting the on-time of the secondswitching signal, the switching signals generated by the first andsecond switching signal generating circuits can be synchronized.

The second switching signal generating circuit may detect lapse timefrom the rising edge of the first switching signal to the rising edge ofthe second switching signal, and change the on-time of the secondswitching signal so that the lapse time becomes close to a predeterminedtarget value. By making the lapse time from the rising edge of the firstswitching signal to the rising edge of the second switching signalconstant, the frequency of the first switching signal and that of thesecond switching signal can be brought close to each other.

The second switching signal generating circuit may make the on-time ofthe second switching signal shift temporally from the on-time of thefirst switching signal. By shifting the on-times of the switchingsignals temporally, the first and second switching elements can beprevented from being turned on simultaneously.

The second switching signal generating circuit may set the predeterminedtarget value so that the on-time of the second switching signal does notoverlap the on-time of the first switching signal. By adjusting thelapse time from the rising edge of the first switching signal to therising edge of the second switching signal, two switching signals can beprevented from being turned on simultaneously.

The first switching signal generating circuit includes: a first voltagecomparator which compares the first output voltage with the firstreference voltage; a first flip flop which is set according to an outputof the first voltage comparator; and a first on-time control circuitwhich resets the first flip flop after lapse of the first on-time fromthe rising edge of an output of the first flip flop, and may output anoutput of the first flip flop as the first switching signal. On theother hand, the second switching signal generating circuit includes: asecond voltage comparator which compares the second output voltage withthe second reference voltage; a second flip flop which is set accordingto an output of the second voltage comparator; and a second on-timecontrol circuit which resets the second flip flop after lapse of thesecond on-time from the rising edge of an output of the second flipflop, and may output an output of the second flip flop as the secondswitching signal, and the second on-time control circuit may detectlapse time from the rising edge of the first switching signal until therising edge of the second switching signal, and change the secondon-time so that the lapse time becomes close to a predetermined targetvalue.

In the second switching signal generating circuit, the rising edge ofthe first switching signal and that of the second switching signal aredetected and, according to the lapse time, the on-time of the secondswitching signal is increased/decreased, thereby changing the timing atwhich the second switching signal is turned on next. In such a manner,the cycle time, that is, the frequency is adjusted, and the secondswitching signal can be synchronized with the first switching signal.

Since the on-time of the first switching signal is constant, “detectionof the lapse time from the rising edge of the first switching signal tothe rising edge of the second switching signal” is equivalent todetection of lapse time from the trailing edge of the first switchingsignal to the rising edge of the second switching signal.

In the second switching signal generating circuit, the second on-timecontrol circuit may shorten the on-time of the second switching signalwhen the lapse time from the rising edge of the first switching signalto the rising edge of the second switching signal is short, and increasethe on-time of the second switching signal when the lapse time is long.

The second on-time control circuit may include: a timer circuit whichflows constant current to a capacitor and measuring, as the on-time ofthe second switching signal, lapse time until voltage reachespredetermined voltage; and an on-time correction circuit whichincreases/decreases the value of the constant current in the timercircuit on the basis of lapse time from the rising edge of the firstswitching signal to the rising edge of the second switching signal.

By changing the value of the constant current for charging the capacitorin the timer circuit, when the constant current is increased, theon-time of the second switching signal can be shortened. When theconstant current is decreased, the on-time of the second switchingsignal can be increased.

The on-time correction circuit may decrease the constant current whenthe lapse time from the rising edge of the first switching signal to therising edge of the second switching signal is short, and increase theconstant current when the lapse time from the rising edge of the firstswitching signal to the rising edge of the second switching signal islong.

The on-time correction circuit may set a correction amount of theconstant current to zero when the lapse time from the rising edge of thefirst switching signal to the rising edge of the second switching signalis about the half of the cycle time of the first switching signal.

Another embodiment of the present invention relates to a switchingregulator. The switching regulator has the switching regulator controlcircuit and a switching element which is turned on/off by the switchingregulator control circuit.

Further another embodiment of the present invention relates to aswitching signal generating apparatus. The apparatus includes: a firstswitching signal generating circuit which generates a first switchingsignal for driving a first switching element; and a second switchingsignal generating circuit which generates a second switching signal fordriving a second switching element. The first switching signalgenerating circuit changes a timing at which the first switching signalis turned on so that first voltage to be controlled becomes close topredetermined first reference voltage, the first voltage being obtainedas a result of switching of the first switching element, while makingon-time of the first switching signal a predetermined constant firston-time. On the other hand, the second switching signal generatingcircuit changes on-time of the second switching signal so that frequencyof the second switching signal becomes close to frequency of the firstswitching signal, and second voltage to be controlled becomes close topredetermined second reference voltage, the second voltage beingobtained as a result of switching of the second switching element.

According to the embodiment, a plurality of switching elements driven bypulse signals can be synchronously controlled.

It is to be noted that any arbitrary combination or rearrangement of theabove-described structural components and so forth is effective as andencompassed by the present embodiments.

Moreover, this summary of the invention does not necessarily describeall necessary features so that the invention may also be asub-combination of these described features.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments will now be described, by way of example only, withreference to the accompanying drawings which are meant to be exemplary,not limiting, and wherein like elements are numbered alike in severalFigures, in which:

FIG. 1 is a circuit diagram showing the configuration of a switchingregulator according to an embodiment.

FIG. 2 is a circuit diagram showing the configuration of a first on-timecontrol circuit.

FIG. 3 is a time chart showing signal waveforms of a first switchingregulator.

FIG. 4 is a circuit diagram showing the configuration of a secondon-time control circuit.

FIG. 5 is a time chart showing signal waveforms of the second on-timecontrol circuit.

FIG. 6 is a time chart showing signal waveforms of a switching regulatorin the case where second on-time is not corrected by an on-timecorrection circuit in the second on-time control circuit.

FIG. 7 is a time chart showing signal waveforms of the switchingregulator in the case where the second on-time is corrected by theon-time correction circuit in the second on-time control circuit.

FIG. 8 is a block diagram showing the configuration of an electronicdevice on which the switching regulator of FIG. 1 is mounted.

DETAILED DESCRIPTION OF THE INVENTION

The invention will now be described based on preferred embodiments whichdo not intend to limit the scope of the present invention but exemplifythe invention. All of the features and the combinations thereofdescribed in the embodiment are not necessarily essential to theinvention.

FIG. 1 shows the configuration of a switching regulator 100 according toan embodiment of the invention. In the following diagrams, the samereference numerals are designated to the same components and repetitivedescription will not be given. FIG. 8 is a block diagram showing theconfiguration of an electronic device 400 on which the switchingregulator 100 of FIG. 1 is mounted. The electronic device 400 is, forexample, a personal computer, a digital appliance, or a battery-poweredsmall-sized information terminal such as a portable telephone terminal,a CD player, or a PDA. In the following embodiments, the electronicdevice 400 will be described as a cellular phone terminal.

The electronic device 400 includes a battery 310, a power supplyapparatus 320, an analog circuit 330, a digital circuit 340, amicroprocessor 350, and an LED 360. The battery 310 is, for example, alithium ion battery and outputs about 3V to 4V as a battery voltage Vbatthat is a DC voltage. The analog circuit 330 includes a circuit blockhaving a power amplifier, an antenna switch, an LNA (Low NoiseAmplifier), a mixer, or a high frequency circuit such as a PLL (PhaseLocked Loop) and stably operating on a power supply voltage Vcc of about3.4V. The digital circuit 340 also includes a circuit block havingvarious DSPs (Digital Signal Processors) and stably operating on a powersupply voltage Vdd of about 3.4V. The microprocessor 350 is a block forcontrolling the whole electronic device 400 in a centralized manner andoperating at a power supply voltage of 1.5V. The LED 360 includes LEDs(Light Emitting Diodes) of three colors of R, G, and B and is used as abacklight of a liquid crystal or illumination. For driving the LED 360,a drive voltage of 4V or higher is required.

The power supply apparatus 320 is a multi-channel switching power supplyincluding a plurality of switching regulators for dropping or boostingthe battery voltage Vbat as necessary on the channel unit basis, andsupplying proper power supply voltages to the analog circuit 330, thedigital circuit 340, the microprocessor 350, and the LED 360. In such apower supply apparatus 320, in the case where the channels perform theswitching operations asynchronously, the switching elements of thechannels may turn on simultaneously. Consequently, the input currentfrom the battery 310 instantaneously increases, and a problem occurssuch that the EMI increases.

By using the switching regulator 100 of FIG. 1 according to theembodiment for a multi-channel power supply apparatus as shown in FIG.8, the switching operations of the channels are synchronized. Thus, aproblem such as EMI can be solved. Referring again to FIG. 1, theconfiguration of the switching regulator 100 according to the embodimentwill be described in detail.

The switching regulator 100 according to the embodiment is astep-down-type DC/DC converter including a master channel and a slavechannel and outputting two output voltages. The switching regulator 100includes a first switching regulator 200 corresponding to the masterchannel, and a second switching regulator 300 corresponding to the slavechannel, and has an input terminal 102, a first output terminal 104, anda second output terminal 106. Each of the first and second switchingregulators 200 and 300 drops an input voltage Vin input to the inputterminal 102, outputs a first output voltage Vout1 from the first outputterminal 104, and outputs a second output voltage Vout2 from the secondoutput terminal 106.

The switching regulator 100 includes a first switching element 12, asecond switching element 22, a first output circuit 14 connected to thefirst switching element 12, a second output circuit 24 connected to thesecond switching element 22, and a switching regulator control circuit1000 for generating switching signals. The switching regulator controlcircuit 1000 includes: a first switching signal generating circuit 10for generating a first switching signal SW1 for driving the firstswitching element 12, and a second switching signal generating circuit20 for generating a second switching signal SW2 for driving the secondswitching element 22, which are integrated.

The first switching regulator 200 includes the first switching signalgenerating circuit 10, the first switching element 12, and the firstoutput circuit 14. Similarly, the second switching regulator 300includes the second switching signal generating circuit 20, the secondswitching element 22, and the second output circuit 24. Since theconfigurations and operations of the first switching regulator 200 andsecond switching regulator 300 are similar, the first switchingregulator 200 will be described below.

The first output circuit 14 includes a first inductor L1 and a firstoutput capacitor Co1 and is connected to the first switching element 12.The first switching element 12 includes a first main transistor Tr1 anda first synchronous rectifier transistor Tr2 connected in series betweenthe input terminal 102 and the ground potential and performed on/offcontrol by drive signals input to the gate terminals of the first maintransistor Tr1 and the first synchronous rectifier transistor Tr2.

The first main transistor Tr1 and the first synchronous rectifiertransistor Tr2 are alternatively turned on/off, thereby supplyingcurrent to the first inductor L1 alternately via the first maintransistor Tr1 and the first synchronous rectifier transistor Tr2, andthe input voltage Vin is dropped. The first inductor L1 and the firstoutput capacitor Co1 forming the first output circuit is a low passfilter, smooth the first output voltage Vout1, and output the smoothedvoltage from the first output terminal 104.

The first switching signal generating circuit 10 includes a firstvoltage comparator 30, a first flip flop 32, a first on-time controlcircuit 34, and a first drive circuit 36.

The first switching signal generating circuit 10 generates the firstswitching signal SW1 for driving the first switching element 12 and, onthe basis of the first switching signal SW1, drives the first switchingelement 12. In the first switching signal generating circuit 10, on-timeTon of the first switching signal SW1 generated by the first switchingsignal generating circuit 10 is constant, and the first switching signalSW1 is a pulse signal whose turn-on timing, that is, frequency changes.

The first switching signal generating circuit 10 generates a switchingsignal whose on-time is constant by the first voltage comparator 30, thefirst flip flop 32, and the first on-time control circuit 34.

The first voltage comparator 30 compares a first reference voltage Vref1and the first output voltage Vout1, and outputs a high-level signal whenthe relation Vref1>Vout1 is satisfied, and outputs a low-level signalwhen the relation Vref1<Vout1 is satisfied. An output VS1 of the firstvoltage comparator 30 is input to a set terminal S of the first flipflop 32. Therefore, the first flip flop 32 keeps the high level of thefirst switching signal SW1 as its output signal during the period sincethe first flip flop 32 is set when the relation Vref1>Vout1 is satisfieduntil the first flip flop 32 is reset.

To the first on-time control circuit 34, an inversion output VQ1′ of thefirst flip flop 32 is input. After a lapse of predetermined time sincethe first flip flop 32 is set, the first flip flop 32 is reset. FIG. 2is a circuit diagram showing the configuration of the first on-timecontrol circuit 34.

The first on-time control circuit 34 is a timer circuit for flowingconstant current to the capacitor and measures a lapse time until avoltage reaches a predetermined voltage. The first on-time controlcircuit 34 includes a first transistor M1, a first capacitor C1, a thirdvoltage comparator 52, and a first constant current source 50.

The inversion output VQ1′ of the first flip flop 32 is input to the gateof the first transistor M1. When the first output voltage Vout1 becomeslower than the first reference voltage Vref1 and the first flip flop 32is set, the inversion output VQ1′ becomes the low level, and the firsttransistor M1 is turned off.

When the first transistor M1 is on state, the first constant currentIon1 generated by the first constant current source 50 flows to theground via the first transistor M1. When the first transistor M1 is offstate, the first capacitor C1 is charged with the first constant currentIon.

Specifically, when the first output voltage Vout1 becomes lower than thefirst reference voltage Vref1 and the first flip flop 32 is set, theinversion output VQ1′ is switched from the high level to the low level,and charging of the first capacitor C1 with the first constant currentIon1 starts.

A voltage Vx appearing at the first capacitor C1 is given by therelation Vx=Ion1/C1×t using a lapse time “t” since the start ofcharging, that is, a lapse time “t” since the first flip flop 32 is set.The third voltage comparator 52 compares the voltage Vx with a thirdreference voltage Vref3. When the relation Vx<Vref3 is satisfied, thethird voltage comparator 52 outputs a low-level signal. When therelation Vx>Vref3 is satisfied, the third voltage comparator 52 outputsa high-level signal. The first on-time control circuit 34 operates as atimer circuit for measuring time since the first flip flop 32 is setand, after a period until the voltage Vx reaches the third referencevoltage Vref3, that is, a predetermined period given by the relationTon1=C1×Vref3/Ion1, sets its output to the high level. As will bedescribed later, the period Ton1 corresponds to on-time of the firstswitching signal SW1. Hereinafter, the predetermined period Ton1 will becalled first on-time.

Referring again to FIG. 1, an output VR1 of the first on-time controlcircuit 34 is input to the reset terminal of the first flip flop 32.Consequently, the first flip flop 32 is reset again after a lapse of thefirst on-time Ton1 since it is set. As a result, the output SW1 of thefirst flip flop 32 becomes the high level for the first on-time Ton1counted by the first on-time control circuit 34.

Setting of the first on-time Ton1 in the first on-time control circuit34 in FIG. 2 will now be described.

As described above, the first on-time Ton1 of the first switching signalSW1 is determined by the first on-time control circuit 34 and given asthe relation Ton1=C1×Vref3/Ion1. The third reference voltage Vref3 isset so as to be equal to or proportional to the first reference voltageVref1 as a target value of the first output voltage Vout1. Further, thevalue of the first constant current Ion1 is set so as to be proportionalto the input voltage Vin. As a result, the relations Vref3=Vref1×b1 andIon1=Vin×a1 are satisfied. It is understood that when they aresubstituted for the first on-time Ton1, the relationTon1=C1×(Vref1×b1)/(Vin×a1) is satisfied.

On the other hand, the relation Ton1=D1×Tp1 is satisfied between firstcycle time Tp1 as the cycle of the first switching signal SW1 and theon-time Ton using the duty ratio D1. The duty ratio D1 in the steadystate of the first switching signal SW1 is given as the relationD1=Vref1/Vin. Therefore, the first cycle time Tp1 is expressed as therelation Tp1=Ton1×Vin/Vref1. When the on-time Ton1 is substituted forthe first cycle time Tp1, the relationTp1=C1×(Vref1×b1)/(Vin×a1)×Vin/Vref1=C1×b1/a1 is obtained. That is, inthe case where a setting is made so that the first constant current Ion1is proportional to the input voltage Vin and the third reference voltageVref3 is proportional to the first reference voltage Vref1, the firstcycle time Tp1 or frequency fp1 given by the inverse number of the firstcycle time Tp1 can be made constant irrespective of the target values ofthe input voltage Vin and the first output voltage Vout1.

FIG. 3 is a time chart showing signal waveforms of the first switchingregulator 200. In the time chart, the axis of ordinate and the axis ofabscissa are shown in scales different from actual ones for easierunderstanding and viewability.

For a period from time T0 to time T1 at which the first switching signalSW1 is off state, the first output voltage Vout1 gradually decreases.When the first output voltage Vout1 becomes lower than the firstreference voltage Vref1 as a target value at the time T1, the output VS1of the first voltage comparator 30 becomes the high level, and the firstflip flop 32 is set.

The first on-time control circuit 34 measures time lapsed since thefirst flip flop 32 is set. In the first on-time control circuit 34, whenthe voltage Vx rises and becomes higher than the third reference voltageVref3 at time T2 after a lapse of the first on-time Ton1 from the timeT1, output VR1 of the third voltage comparator 52 becomes the highlevel, and the first flip flop 32 is reset. During the on-time of thefirst switching signal SW1 from the time T1 to the time T2, the firstoutput voltage Vout1 rises. After that, when the first switching signalSW1 is turned off, the first output voltage Vout1 starts decreasingagain and becomes lower than Vref1 (Vout1<Vref1) at time T3, and thefirst flip flop 32 is set again, and the first switching signal SW1 isturned on.

As described above, the first switching signal generating circuit 10generates the first switching signal SW1 while making the on-time thepredetermined constant first on-time Ton1 and changing the on timing sothat the first output voltage Vout1 becomes close to the predeterminedfirst reference voltage Vref1.

The first switching signal SW1 is input to the first drive circuit 36,and the first drive circuit 36 generates a drive signal for driving thefirst switching element 12 on the basis of the first switching signalSW1. In the embodiment, a drive voltage is generated so that the firstmain transistor Tr1 is turned on in the on-time of the first switchingsignal SW1 and the first synchronous rectifier transistor Tr2 is turnedon in the off time of the first switching signal SW1. As a result, thefirst output voltage Vout1 is controlled so as to be close to the firstreference voltage Vref1.

Referring again to FIG. 1, the second switching regulator 300 as a slavechannel will be described. Since the basic configuration and operationof the second switching regulator 300 are similar to those of the firstswitching regulator 200, the different points will be mainly describedbelow.

The second switching regulator 300 includes the second switching signalgenerating circuit 20, the second switching element 22, and the secondoutput circuit 24. The configurations and operations of the secondswitching element 22 and the second output circuit 24 are similar tothose of the first switching element 12 and the first output circuit 14,respectively.

The second switching signal generating circuit 20 includes a secondvoltage comparator 40, a second flip flop 42, a second on-time controlcircuit 44, and a second drive circuit 46. Since the configurations andoperations of the second voltage comparator 40, the second flip flop 42,and the second drive circuit 46 are similar to those of the firstswitching signal generating circuit 10, the second on-time controlcircuit 44 will be described below.

The second on-time control circuit 44 resets the second flip flop 42after a lapse of second on-time Ton2 from the time the second flip flop42 is set to the time the second switching signal SW2 is to be turnedon. To the second on-time control circuit 44, the first switching signalSW1 is input in addition to an inversion output VQ2′ of the second flipflop 42 to the second on-time control circuit 44. On the basis of thelapse time from the rising edge of the first switching signal SW1 to therising edge of the second switching signal SW2, the on-time Ton2 of thesecond switching signal SW2 is changed.

FIG. 4 is a circuit diagram showing the configuration of the secondon-time control circuit 44. The second on-time control circuit 44includes a timer circuit 80 and an on-time correction circuit 70.

The configuration and operation of the timer circuit 80 are similar tothose of the first on-time control circuit 34 in FIG. 2. In the diagram,a second capacitor C2 is charged with charging current shown by Ich2 inthe diagram, and time required for voltage Vy appearing in the secondcapacitor C2 to reach predetermined fourth reference voltage Vref4 ismeasured. Therefore, time measured by the timer circuit 80 is expressedas the relation Ton2=C2×Vref4/Ich2.

The on-time correction circuit 70 outputs synchronous correction currentIsync. The charging current Ich2 for charging the second capacitor C2 isgiven by the sum of second constant current Ion2 output from a secondconstant current source 60 and the synchronous correction current Isyncoutput from the on-time correction circuit 70, and the relationIch2=Ion2+Isync is satisfied. Therefore, when the synchronous correctioncurrent Isync is positive, the second on-time Ton2 measured by the timercircuit 80 becomes short. When the synchronous correction current Isyncis negative, the second on-time Ton2 becomes long. That is, by changingthe value of the synchronous correction current Isync, the on-timecorrection circuit 70 can adjust the second on-time Ton2. In thefollowing, the second on-time will be distinguished as follows. Thesecond on-time when the correction amount Isync=0 will be calledreference second on-time Ton2, and the second on-time after correctionof the on-time correction circuit 70 will be called corrected secondon-time Ton2′.

Also in the second on-time control circuit 44, like the first on-timeTon1 in the first on-time control circuit 34, the reference secondon-time Ton2 is set so that second cycle time Tp2 as the cycle of thesecond switching signal SW2 becomes constant irrespective of the inputvoltage Vin and second reference voltage as a target value of the outputvoltage.

Specifically, a setting is made so that the second constant current Ion2is proportional to the input voltage Vin and the fourth referencevoltage Vref4 is proportional to the second reference voltage Vref2 asthe target value of the second output voltage Vout2. When the secondconstant current Ion2 is equal to Vin×a2 and the fourth referencevoltage Vref4 is equal to b2×Vref2, the second cycle time Tp2 becomesequal to C2×b2/a2 and can be made constant irrespective of the inputvoltage Vin and the target value of the second output voltage Vout2.

In the embodiment, constants are determined so that the relationC1×b1/a1=C2×b2/a2 is satisfied in the first on-time control circuit 34and second on-time control circuit 44. In this case, in an ideal circuitin which power losses in the inductors and capacitors used for the firstoutput circuit 14 and second output circuit 14, the first switchingelement 12, and the second switching element 22 can be ignored, thefirst cycle time Tp1 of the first switching signal SW1 and the secondcycle time Tp2 of the second switching signal SW2 in the steady statecan be made equal to each other, that is, the frequency of the firstswitching signal SW1 and that of the second switching signal SW2 can bemade equal to each other.

In an actual circuit, however, resistive components are included in theelements and the elements have variability. Also in the case where therelation C1×b1/a1=C2×b2/a2 is satisfied, a slight difference occursbetween the frequency fp1 of the first switching signal SW1 and thefrequency fp2 of the second switching signal SW2. The on-time correctioncircuit 70 adjusts the length of the reference second on-time Ton2 ofthe second switching signal SW2 so that the frequency fp2 of the secondswitching signal becomes close to the frequency fp1 of the firstswitching signal. For this purpose, the synchronous correction currentIsync is generated on the basis of the lapse time from the rising edgeof the first switching signal SW1 to the rising edge of the secondswitching signal SW2. As shown in FIG. 4, the on-time correction circuit70 includes a one-shot circuit 68, a third transistor M3, a thirdconstant current source 66, a third capacitor C3, an operationalamplifier 64, transistors Q1, Q2, and Q3, and a fourth constant currentsource 72.

The first switching signal SW1 is input to the one-shot circuit 68. Theone-shot circuit 68 continuously holds its output at the high level fora predetermined period since the first switching signal SW1 is turnedon. An output of the one-shot circuit 68 is connected to the gate of thethird transistor M3 as an N-type MOSFET transistor. When an output ofthe one-shot circuit 68 becomes the high level, the third transistor M3is turned on to discharge the third capacitor C3, thereby droppingvoltage Vz appearing in the third capacitor C3 to 0V.

The third constant current source 66 is connected to the third capacitorC3 to supply the constant current Ib. The voltage Vz appearing at thethird capacitor C3 rises in proportional to time by charging with theconstant current Ib and is expressed as the relation Vz=Ib/C3×t usingthe lapse time “t” from start of the charging. The third capacitor C3 isconnected to the non-inverting input terminal of the operationalamplifier 64.

The output of the operational amplifier 64 is connected to the base ofthe transistor Q3, and the inverting input terminal is connected to theemitter of the transistor Q3. A resistor R1 is provided between theemitter of the transistor Q3 and the ground. A feedback is performed sothat the voltage of the non-inverting input terminal and that of theinverting input terminal of the operational amplifier 64 become equal toeach other. Consequently, the voltage Vz appears at the connection pointbetween the resistor R1 and the transistor Q3. As a result, the currentId given by Vz/R1 flows to the resistor R1.

The transistors Q1 and Q2 form a current mirror circuit, and the fourthconstant current source 72 for generating the constant current Ic isconnected to the collector of the transistor Q1. As a result, thedifference between the constant current Ic and the current Id is outputas the synchronous correction current Isync from the on-time correctioncircuit 70. The synchronous correction current Isync is the function ofthe lapse time “t” from the rising edge of the first switching signalSW1 and is expressed as the relationIsync(t)=Id−Ic=Vz/R1−Ic=(Ib/C3/R1)×t−Ic.

Since the synchronous correction current Isync is the function of time,the charging current Ich2 is given as the function of time and can beexpressed as the relation Ich2(t)=Ion2+Isync(t).

The charging of the second capacitor C2 starts from the rising edge ofthe second switching signal SW2. When it is assumed that the secondswitching signal SW2 rises at time t1, the voltage Vy at time t2 isproportional to a value obtained by integrating the charging currentIch2 from the time t1 to the time t2. When it is assumed that thevoltage Vy reaches the fourth reference voltage Vref4 at the time t2,the corrected second on-time Ton2′ is given by t2−t1.

Since the time at which the first switching signal SW1 rises correspondsto t=0, the time t1 at which the second switching signal SW2 risescorresponds to lapse time from the rising edge of the first switchingsignal SW1 to the rising edge of the second switching signal SW2.

The corrected second on-time Ton2′ is obtained by solving an equationderived by the integration, and changes according to the lapse time t1from the rising edge of the first switching signal SW1 to the risingedge of the second switching signal SW2. When the lapse time t1 is long,the corrected second on-time Ton2′ is long. On the contrary, when thelapse time t1 is short, the corrected second on-time Ton2′ is short.

FIG. 5 is a time chart showing current and voltage waveforms of thesecond on-time control circuit 44.

At time T1, the first switching signal SW1 is turned on. At this time,the one-shot circuit 68 is on state for a predetermined period, so thatthe charge accumulated in the third capacitor C3 are discharged and thevoltage Vz appearing at the third capacitor C3 decreases to 0V. When theone-shot circuit 68 is turned off, the third capacitor C3 is chargedwith the constant current Ib, and the voltage Vz rises at the gradientof Ib/C3. The current Id flowing in the resistor R1 increases with timein proportion to the voltage Vz.

When attention is paid to the synchronous correction current Isync, therelation Isync=Id−Ic is satisfied. Therefore, at the time T1 when therelation Id=0 is satisfied, Isync becomes −Ic that is a negative value.After that, as the current Id increases, the synchronous correctioncurrent Isync increases from the negative value to a positive value. Thesynchronous correction current Isync is adjusted in advance so as tobecome zero at time T3 after a lapse of Tp1/2 as the half of the cycletime Tp1 of the first switching signal SW1 from the time T1.

The current Id increases with time at the gradient Ib/(C3×R1), and thegradient of the synchronous correction current Isync becomes equal tothe gradient Ib/(C3×R1). It is sufficient to increase the synchronouscorrection current Isync only by Ic in the time Tp1/2 which is the halfof the cycle time of the first switching signal SW1. It is thereforesufficient to determine the current value Ib, the resistance R1, and thecapacitance value C3 so that the relation Ic=Ib/(C3×R1)×Tp1/2 issatisfied.

In the case where the synchronous correction current Isync is generatedin the on-time correction circuit 70 as described above, the chargingcurrent Ich2 in the timer circuit 80 becomes current obtained by addingthe synchronous correction current Isync that changes with time to thesecond constant current Ion2 generated by the second constant currentsource 60.

The operation of the switching regulator 100 having the aboveconfiguration will be described. In the following description, it isassumed that the input voltage Vin is 10V, the first reference voltageVref1 is 2V, and the second reference voltage Vref2 is 2.5V. The dutyratio D1 of the first switching signal SW1 in the steady state is 20%,and the duty ratio D2 of the second switching signal SW2 is 25%.

First, to make the effects of the invention clearer, the operation inthe case where the second on-time is not corrected by the on-timecorrection circuit 70 in the second on-time control circuit 44 will bedescribed.

FIG. 6 is a time chart showing signal waveforms of the switchingregulator 100 in the case where the second on-time is not corrected bythe on-time correction circuit 70 in the second on-time control circuit44.

As described above, it is set so that the frequency of the firstswitching signal SW1 and that of the second switching signal SW2 becomeequal to each other in an ideal state in the first on-time controlcircuit 34 and second on-time control circuit 44. In an actual circuit,however, resistive components are included in the elements in thecircuit and the elements also have variability, so that a differenceoccurs between the cycle times Tp1 and Tp2 of the first switching signalSW1 and second switching signal SW2. Since the on/off operation of thesecond switching signal SW2 repeats independently of the first switchingsignal SW1, the lapse time td from the rising edge of the firstswitching signal SW1 to the rising edge of the second switching signalSW2 a (hereinbelow, simply called the lapse time td) varies amongcycles. The on-times overlap at timings shown in a hatched portion inFIG. 6, and a problem such as increase in EMI occurs.

Next, the operation performed in the case of correcting the secondon-time by the on-time correction circuit 70 in the second on-timecontrol circuit 44 will be described.

FIG. 7 is a time chart showing signal waveforms of the switchingregulator 100 in the case of correcting second on-time by the on-timecorrection circuit 70 in the second on-time control circuit 44.

The first switching regulator 200 as the master channel is in the steadystate in which the first output voltage Vout1 is stably output, andon-time and off time appear repeatedly at the duty ratio of 20%.

At time T1, the first switching signal SW1 is turned on. After that,when the second output voltage Vout2 drops to the second referencevoltage Vref2 at time T2, the second switching signal SW2 is turned on.When the second switching signal SW2 is turned on, the corrected secondon-time Ton2′ of the second switching signal SW2 is determined by thesecond on-time control circuit 44 in the second switching signalgenerating circuit 20.

As described above, in the second on-time control circuit 44, when thefirst switching signal SW1 rises, the charging current Ich2 for chargingthe second capacitor C2 in the timer circuit 80 starts increasinggradually. At time T2 at which the second switching signal SW2 rises,the charging current Ich2 is smaller than the second constant currentIon2. As a result, time required to charge the second capacitor C2 tothe fourth reference voltage Vref4, that is, the corrected secondon-time Ton2′ becomes longer than the reference second on-time Ton2. Thesecond on-time control circuit 44 resets the second flip flop 42 andturns off the second switching signal SW2 at time T3 after a lapse ofthe corrected second on-time Ton2′ since the second switching signal SW2is turned on. During the on-time of the second switching signal SW2 fromthe time T2 to the time T3, the second output voltage Vout2 rises. Whenthe second switching signal SW2 is turned off at the time T3, the secondoutput voltage Vout2 starts dropping.

At time T4, the first switching signal SW1 is turned on again. Duringthe time, the second output voltage Vout2 gradually decreases. At timeT5 at which the second output voltage Vout2 drops to the secondreference voltage Vref2, the second switching signal SW2 is turned on.Since the corrected second on-time Ton2′ of last time was set to belonger than the reference second on-time Ton2, lapse time td2 from therising edge of the first switching signal SW1 to the rising edge of thesecond switching signal SW2 becomes longer than the lapse time td1 oflast time, and the rising of the second switching signal SW2 is delayed.

When the second switching signal SW2 is turned on at the time T5, thesecond on-time Ton2 is adjusted again by the second on-time controlcircuit 44. Since the charging current Ich2 at the time T5 at which thesecond switching signal SW2 rises is lower than the second constantcurrent Ion2, the corrected second on-time Ton2′ becomes longer thanreference second on-time Ton2. The second switching signal SW2 is turnedoff at time T6.

The first switching signal SW1 is turned on again at time T7, and thesecond switching signal SW2 is turned on at time T8. By adjustingcorrected second on-time Ton2″ of last time, the lapse time td3 from therising edge of the first switching signal SW1 to the rising edge of thesecond switching signal SW2 becomes longer than the lapse time td2.

The correction amount of the second on-time Ton2 is determined by thesynchronous correction current Isync, and the synchronous correctioncurrent Isync is set to become zero after a lapse of the half of thefirst cycle time Tp1 from the first switching signal SW1. Therefore, thetime of the rising edge of the second switching signal SW2 is graduallyadjusted and converges to the time which is after a lapse of Tp1/2 fromthe rising edge of the first switching signal SW1.

As described above, in the switching regulator 100 according to theembodiment, the on-time Ton2 of the second switching signal SW2 iscorrected according to the lapse time from the rising edge of the firstswitching signal SW1 to the rising edge of the second switching signalSW2, and the switching element is driven in accordance with thecorrected on-time Ton2′. Consequently, the cycle time of the firstswitching signal SW1 and that of the second switching signal SW2 arebrought close to each other and the first switching signal SW1 andsecond switching signal SW2 can be synchronized.

In the on-time correction circuit 70 in the second on-time controlcircuit 44, by setting the correction amount of the charging currentIch2 to zero at time after the half of the cycle time of the firstswitching signal SW1 from the rising edge of the first switching signalSW1, the on-time of the first switching signal SW1 and that of thesecond switching signal SW2 are shifted temporally. The first switchingsignal SW1 and second switching signal SW2 are repeatedly turned on/offwhile their phases shift from each other by 180 degrees.

As a result, the first switching signal SW1 and second switching signalSW2 can be prevented from being turned on at the same time,instantaneous increase in the input current flowing in the inputterminal 102 is prevented, and the current capacitance of the powersupply connected to the input terminal 102 can be reduced. Further, thecapacitance of an input capacitor for smoothing which is connected tothe input terminal 102 can be reduced or made unnecessary. In addition,since instantaneous increase in the input current can be suppressed, theinfluence of EMI on the circuit can be reduced, and the circuit canoperate stably.

It is understood by a person skilled in the art that the embodiment isillustrative, the components and combinations of processes can bevariously modified, and such modifications are within the scope of thepresent invention.

For example, in the first on-time control circuit 34 and second on-timecontrol circuit 44 in the embodiment, the third reference voltages Vref3and fourth reference voltage Vref4 are made proportional to the firstreference voltage Vref1 and second reference voltage Vref2,respectively, and the first constant currents Ion1 and second constantcurrent Ion2 are made proportional to the first reference voltage Vref1and second reference voltage Vref2, respectively, so that the firstcycle time Tp1 and the second cycle time Tp2 in the ideal state becomeequal to each other. In the present invention, however, it is not alwaysnecessary to set the first and second cycle times Tp1 and Tp2 to beequal to each other. Since the second on-time Ton2 of the secondswitching signal SW2 is corrected by feedback in the on-time correctioncircuit 70 in the second on-time control circuit 44, the two cycle timesare brought close to each other, and a synchronization control can beperformed.

Although a setting is made so that the synchronous correction currentIsync becomes zero after the lapse of the half of the first cycle timeTp1 from the rising edge of the first switching signal SW1 in theforegoing embodiment, the setting does not always have to be made to thehalf of the cycle time. In the second on-time control circuit 44, thefeedback control is performed so that the second switching signal SW2 isturned on when the synchronous correction current Isync becomes zeroafter the rising edge of the first switching signal. Therefore, bymaking a setting so that the synchronous correction current Isyncbecomes zero at time the second switching signal SW2 is desired to beturned on, the on-time can be arbitrarily shifted.

Although the case where the synchronous correction current Isyncgenerated by the on-time correction circuit 70 depends on the lapse timetd from the riding edge of the first switching signal and the chargingcurrent Ich2 also changes with time as shown in FIG. 5 has beendescribed in the embodiment, the invention is not limited to the case.For example, the synchronous correction current Isync is specified asthe function of the lapse time td as shown in FIG. 5, and the value ofthe synchronous correction current Isync at the rising time of thesecond switching signal SW2 is set as a synchronous correction currentvalue. By adding the synchronous correction current value to the secondconstant current Ion2, the charge current Ich2 may be obtained. In thiscase as well, the corrected second on-time Ton2 is unconditionallydetermined for the lapse time td, the rising time of the secondswitching signal SW2 can be converged to time when the synchronouscorrection current Isync becomes zero by feedback, and the secondswitching signal SW2 can be synchronized with the first switchingsignal.

In the embodiment, the first on-time control circuit 34 and secondon-time control circuit 44 for setting on-time of the first switchingsignals SW1 and second switching signal SW2, respectively, are formed byanalog circuits. Alternately, the circuits may be formed by timercircuits of another form or digital circuits.

Also in the case where the second on-time control circuit 44 is formedby a digital circuit, it is sufficient to determine the second on-timeTon2 as the function of the lapse time td, and operations similar tothose of the second on-time control circuit 44 according to theembodiment can be performed.

Although the switching regulator 100 having outputs of two channels hasbeen described as an example in the embodiment, the invention can bealso applied to a switching regulator having three channels of a masterchannel, a first slave channel, and a second slave channel.

In this case, the on-time correction circuit is provided for the on-timecontrol circuit in each of the first slave channel and second slavechannel, the switching signal of the first slave channel is controlledto rise after a lapse of ⅓ of the cycle time of a switching signal ofthe master channel from the rising edge of the switching signal, and aswitching signal of the second slave channel is controlled to rise aftera lapse of ⅔ of the cycle time. In such a manner, the number of channelscan be increased.

In the embodiment, all of elements forming the switching regulator 100may be integrated or formed in a plurality of integrated circuits.Further, a part of the elements may be a discrete part.

For example, the switching regulator control circuit 1000 of theembodiment may be integrated with the first switching element 12 and thesecond switching element 22. Which part is to be integrated may bedetermined in accordance with specifications, cost, occupation area, andthe like requested for the circuit.

In the embodiment, the step-down switching regulator has been described.In the step-down switching regulator, the first synchronous rectifiertransistor Tr2 and second synchronous rectifier transistor Tr4 may berectifier diodes. The invention is not limited to the step-downswitching regulator but can be also applied to a boosting switchingregulator or boosting/step-down switching regulator. The invention canbe also applied to a switched-capacitor-type DC/DC converter and can bewidely applied to a power supply apparatus in which a switching elementis switching-controlled by a pulse signal.

In the circuit configuration of each of the blocks in the embodiment, aMOSFET and a bipolar transistor can be freely replaced with each other.It is sufficient to determine which transistor to be used in accordancewith design specifications requested for the circuit, semiconductormanufacturing processes used, and the like.

The invention can be applied also to a drive circuit for driving a motorby supplying a pulse signal to a switching transistor as a component ofan H bridge circuit or the like. The invention can be widely applied toa control circuit for driving a switching element driven by pulsemodulation.

While the preferred embodiments of the present invention have beendescribed using specific terms, such description is for illustrativepurposes only, and it is to be understood that changes and variationsmay be made without departing from the spirit or scope of the appendedclaims.

1. A switching regulator control circuit comprising: a first switching signal generating circuit which generates a first switching signal for driving a first switching element connected to a first output circuit; and a second switching signal generating circuit which generates a second switching signal for driving a second switching element connected to a second output circuit, wherein the first switching signal generating circuit changes a timing at which the first switching signal is turned on so that first output voltage output from the first output circuit becomes close to predetermined first reference voltage while making on-time of the first switching signal predetermined constant first on-time, and the second switching signal generating circuit changes on-time of the second switching signal so that frequency of the second switching signal becomes close to frequency of the first switching signal, and changes a timing at which the second switching signal is turned on so that second output voltage output from the second output circuit becomes close to predetermined second reference voltage, wherein the first switching signal generating circuit comprises: a first voltage comparator which compares the first output voltage with the first reference voltage; a first flip flop which is set according to an output of the first voltage comparator; and a first on-time control circuit which resets the first flip flop after lapse of the first on-time from the rising edge of an output of the first flip flop, and outputs an output of the first flip flop as the first switching signal, and the second switching signal generating circuit comprises: a second voltage comparator which compares the second output voltage with the second reference voltage; a second flip flop which is set according to an output of the second voltage comparator; and a second on-time control circuit which resets the second flip flop after lapse of the second on-time from the rising edge of an output of the second flip flop, and outputs an output of the second flip flop as the second switching signal, and the second on-time control circuit detects lapse time from the rising edge of the first switching signal to the rising edge of the second switching signal, and changes the second on-time so that the lapse time becomes close to a predetermined target value.
 2. The switching regulator control circuit according to claim 1, wherein the second switching signal generating circuit detects lapse time from the rising edge of the first switching signal to the rising edge of the second switching signal, and changes the on-time of the second switching signal so that the lapse time becomes close to a predetermined target value.
 3. The switching regulator control circuit according to claim 2, wherein the second switching signal generating circuit sets the predetermined target value so that the on-time of the second switching signal does not overlap the on-time of the first switching signal.
 4. The switching regulator control circuit according to claim 1, wherein the second on-time control circuit comprises: a timer circuit which flows constant current to a capacitor and measuring, as the on-time of the second switching signal, lapse time until voltage reaches predetermined voltage; and an on-time correction circuit which increases/decreases the value of the constant current in the timer circuit on the basis of lapse time from the rising edge of the first switching signal to the rising edge of the second switching signal.
 5. The switching regulator control circuit according to claim 4, wherein the on-time correction circuit decreases the constant current as the lapse time from the rising edge of the first switching signal to the rising edge of the second switching signal is short, and increases the constant current as the lapse time from the rising edge of the first switching signal to the rising edge of the second switching signal is long.
 6. The switching regulator control circuit according to claim 5, wherein the on-time correction circuit sets a correction amount of the constant current to zero when the lapse time from the rising edge of the first switching signal to the rising edge of the second switching signal is about the half of the cycle time of the first switching signal.
 7. A switching regulator comprising the switching regulator control circuit according to claim 1, and a switching element which is turned on/off by the switching regulator control circuit.
 8. An electronic device comprising a voltage source which generates a predetermined DC voltage, and the switching regulator according to claim 7 which boosts or drops the DC voltage and outputs the resultant voltage to a load.
 9. A switching signal generating apparatus comprising: a first switching signal generating circuit which generates a first switching signal for driving a first switching element; and a second switching signal generating circuit which generates a second switching signal for driving a second switching element, wherein the first switching signal generating circuit changes a timing at which the first switching signal is turned on so that first voltage to be controlled becomes close to predetermined first reference voltage, the first voltage being obtained as a result of switching of the first switching element, while making on-time of the first switching signal predetermined constant first on-time, and the second switching signal generating circuit changes on-time of the second switching signal so that frequency of the second switching signal becomes close to frequency of the first switching signal, and second voltage to be controlled becomes close to predetermined second reference voltage, the second voltage being obtained as a result of switching of the second switching element, wherein the first switching signal generating circuit comprises: a first voltage comparator which compares the first output voltage with the first reference voltage; a first flip flop which is set according to an output of the first voltage comparator; and a first on-time control circuit which resets the first flip flop after lapse of the first on-time from the rising edge of an output of the first flip flop, and outputs an output of the first flip flop as the first switching signal, and the second switching signal generating circuit comprises: a second voltage comparator which compares the second output voltage with the second reference voltage; a second flip flop which is set according to an output of the second voltage comparator; and a second on-time control circuit which resets the second flip flop after lapse of the second on-time from the rising edge of an output of the second flip flop, and outputs an output of the second flip flop as the second switching signal, and the second on-time control circuit detects lapse time from the rising edge of the first switching signal to the rising edge of the second switching signal, and changes the second on-time so that the lapse time becomes close to a predetermined target value. 